In the wide world of wristwatches, there’s no easier way to dress aesthetically or personalize your timepiece than by swapping straps and bands. There are all kinds of bands out thereby nylon NATOs And leather dangle straps Unpleasant hotly debated metal link bracelets. Most watch straps are universal for traditional watches of similar size, an open ecosystem for anyone to explore.

But none are as simple and convenient as the patented little band release buttons on the bottom of every Apple Watch.

While I often prefer a universal solution to a proprietary connector, here’s the problem: Apple’s band release button beats the fiddling with little spring pins and jewelers’ tools. Instead, you just press an almost invisible button, slide your band out, slide another in, and get a nice audible click as it clicks into place. No fuss, no fuss; just a simple swap for a different visual vibe to suit your style and wardrobe.

But how does it get that precise click, that almost foolproof click? Tip: They are not magnets. My colleague Sean Hollister and I talked to two ex-Apple engineers who worked on the manufacturing of the original parts. We quickly learned that it’s a bit of the unsung hero of the Apple Watch – despite launching a $1 billion accessory ecosystem and remaining unchanged since its debut eight years ago.

The secret: they actually exist three buttons in the Apple Watch, two of which interlock so precisely that Apple had to rethink its entire approach to manufacturing. “The tolerances there are kind of insane,” our sources say. “It’s super hard to edit. You can’t get tools in it; the angles are all weird. So in the end, the company bought Swiss CNC machines that cost up to $2 million – each – just for the sake of the interchangeable belt system. “It didn’t cut anything else on the watch, just this, that’s all it did.”

Internally, Apple calls the assembly X206, and that makes changing bands on the Apple Watch effortless.

When you start to slide the strap into the slot of your watch, the bezel of the watch touches Button No. 1: a spring-loaded tooth. The prong is rounded just enough that the watch pushes it into a hollow in the band instead of being stuck. There it compresses two small springs to build pressure against Button No. 2: a flat oval with a polished finish held by Button No.’s miniature hooks. 1. As you slide the band into your watch, both buttons hold together for a moment – until the No. 2 button aligns with the precision-cut locking groove in the base of your watch.

Then, with that satisfying click, the force of the springs pressed by the No. 1 button pushes the No. 2 button into that groove and it clicks into place.

Change bands? Pressing the strap release button (Button No. 3) pushes the No. 2 button out of the groove, allowing your belt to slide freely by pushing the No. 2 button back into the No. 1 button. It’s like Apple took the conventional spring pins from traditional watches, miniaturized them, flipped them on their side, and embedded them into the watch band.

Technically, Apple’s little springs have enough force to push the No. 2 button back into its groove as soon as you let go of the band release button. But the groove is so precisely cut that once you start sliding your strap out of the watch, you’re out of danger.

How exactly are we talking? Well, for a little perspective, a human hair is about 70 microns thick, and a regular CNC can cut to about plus or minus 50 microns. As for the fancy-schmancy Swiss CNCs for cutting the Apple Watch band slot? The accuracy is plus or minus five microns, say the ex-Apple engineers. Even with that precision, “the amount of finished watch cases and straps they’ve thrown away for failing to meet these exacting tolerances is an inordinate amount. It’s not a small number.”

Apple has bought hundreds of multimillion-dollar CNC machines, ex-engineers say. “At the time, Rolex was the largest buyer of these machines. And then Apple bought more than anyone had ever bought, including Rolex up to that point.” But you don’t become a watchmaker overnight by buying CNC machines under Rolex’s nose. “The number of people who lived in the factory to get these machines running, sleeping bags on the floor 24/7, is not zero. People’s whole lives to get that one lock perfect.”

Then there’s the mounting to consider, because there are actually those four springs in each watch band. The other two hold all parts of the mechanism in place so that they do not fall out of the cavity.

“If you get a pin, you can take it out and take it apart [but] you won’t be able to put it back together. It’s absolutely miniature, and Apple actually had to design an entire automation process to put it together. This is all automated mounting, where these tiny springs are inserted, the tooth is pushed through, the two horizontal springs are placed on the clip to provide the pressure to hold that little clip in the tooth,” they say.

This may also seem like an exorbitant amount of effort and investment for some watch straps, but it seems to have paid off. “Apple created an entirely new business category. This whole ecosystem of interchangeable tires; that is a billion dollar business for them.”

It almost didn’t happen this way. Jony Ive originally wanted a single strap with magnets, they say.

Something must have changed his mind, but still he described the mechanism because he has “a sophistication and precision that comes from functionality” when introducing the first Apple Watch, neither he nor Apple ever really explained how long it took to make Apple Watch bands what they are. “People don’t appreciate the kind of artistry of what we’ve done here,” says an ex-engineer.

But Apple does a smart job of introducing owners to the band release button and interchangeable bands when they first open the box. If you bought an Apple Watch after the first few Series models, you know that the watch and band are not pre-attached. Part of this is logistical: the sheer number of SKUs required for all sizes, variations, and bands of the Apple Watch. But you also learn by doing, and a well-known former editor of the world’s most influential watch publication thinks Apple might want to educate the masses about a little piece of watchmaking.

“Most watch users don’t know how to change the band and I bet many before Apple Watch didn’t know this was an option. I think Apple popularized strap swapping outside of the watch enthusiast audience,” said Stephen Pulvirent, founder of communications firm Rime & Reason and former editor of Hodinkeetells The edge.

Even within the enthusiast crowd, changing straps on traditional watches can be a pain. Some traditional straps may have exposed spring pins that you can easily remove with a fingernail, but many straps require small tools – with varying degrees of difficulty (and risk of scratching your timepiece).

As much as I personally like traditional watches, I have to admit that Apple’s method is simpler, more accessible, and just downright better. And while many of Apple’s own bands are pricey, there’s also a huge ecosystem of third-party options available (and not just imitations on Amazon). There are boutique manufacturers – even Etsy sellers – create their own unique bands. Want to accessorize your Apple Watch with an elastic nylon band with funky patterns? No problem. A leather strap reminiscent of a studded punk bracelet? Don’t ask me why I know, believe me when I say it they are out there. You can pay more or less as high a price as you want – the world is your patina.

The Apple Watch’s larger ecosystem of bands, bands, and bracelets — from Apple and beyond — are as good as they come, thanks in part to Apple’s over-engineering of that nifty little unlock button. There are so many ways to match your style or personal flair and dress up or dress up that little rounded computer on your wrist, and you don’t have to be image obsessed or progressive to appreciate that. Whether you wear an Apple Watch all the time, occasionally, or even if you’re a crazy kid who pairs it with a regular watch, a touch of personal expression is just a touch away.